Many power generation plants produce electricity by converting energy (e.g. fossil fuel, nuclear fission, hydraulic head, geothermal heat) into mechanical energy (e.g. rotation of a turbine shaft), and then converting the mechanical energy into electrical energy (e.g. by the principles of electromagnetic induction). For example, fossil fuel power generation plants typically use a turbine to convert the fossil fuel into mechanical energy and a generator to convert the mechanical energy into electricity.
One aspect of the above-described power generation scheme involves conductive copper coils located within axially extending slots of the generator's rotor (FIG. 1). The rotor coils carry a DC current, from which an AC current is induced. The rotor coils comprise individual copper strands that are separated by insulation to prevent electrical arcing, among other reasons. Slot cell or other types of insulation may also be used to sheath the entire rotor coil or portions thereof. The insulated coils are then usually wedged within the slots to inhibit vibration.
The manufacture of rotor coils typically involves the steps shown in FIG. 2. Nascent insulated strands are first “laid-up” by arranging an adhesive between a strand of conductive copper and a strand of insulation (Step 1). The copper/adhesive/insulation layer is then sandwiched by a padding to more uniformly distribute the heat and pressure to be applied during the subsequent press cycle. The padding/copper/adhesive/insulation/padding layering is then repeated about 5-20 times to form a plurality of stacks. The stacks are then loaded into a press (Step 2), and the press ramped up from room condition to about 500-1,000 PSI and about 100-200° C. within about 15-45 minutes (Step 3). The nascent coils are then allowed to dwell for about 20-40 minutes within the press (Step 4), and the press is then ramped back down to room condition within about 15-45 minutes (Step 5).
The press cycle cures the adhesive and provides adherence with the copper and insulation. The cured stacks are then unloaded from the press and unstacked to the 5-20 separate stacks or insulated strands (Step 6). The insulated strands can then be assembled into the rotor coils, and the rotor coils wedged into the rotor slots (Step 7) to perform the intended purpose of carrying DC current.
However, there are several disadvantages of this prior art rotor coil manufacturing process. One disadvantage involves the costly and time-consuming nature of such manufacturing process. For example, the lay-up process takes about ½ man hour to complete, the pressing process takes about 1½ man-hours to complete, and the unloading and unstacking process takes about ½ man-hour to complete. Thus, it takes a total of about 2½ man-hours to manufacture about 5-20 insulated strands. Another disadvantage involves physical and electrical variations among insulated strands. For example, the location of the strands and adhesive relative to the press can cause the strands and adhesive to receive different amounts of heat and pressure for different amounts of time, with those closer to the press receiving higher amounts of heat and pressure which can overcure the adhesive, while those farther from the press receiving lower amounts of heat and pressure which can undercure the adhesive.
There is thus a need to reduce the amount of time and cost needed to manufacture rotor coils. There is also a need to reduce variation among insulated strands. There is also a need for a tacking application that improves upon the prior art.